Four Lessons I Have Learned From Physiology

And how they can make you a faster runner

One of the things I love most about the sport of distance running is that, in spite of its simplicity of putting one foot in front of the other, it is also extremely complex. When done correctly, it is a scientific endeavor to maximize one's speed and endurance. Unfortunately, nearly all scientists spend their careers in academia without venturing out into the arena that got many of them interested in physiology in the first place -- competitive sport. As a result, few scientists are coaches. The opposite is also true -- few coaches are scientists. Being both, I have learned that each can learn from the other, as my experience has given me a unique view of the sport and of the training process. Here are four lessons I have learned from physiology and how they can make you a faster runner.

Physiology lesson 1.0

Lactate threshold and running economy are more important than VO2 max.What It Means For You: Threshold training (tempo runs), high mileage, and power workouts are more important than long intervals, especially once your VO2 max has plateaued.

While VO2 max (the maximum volume of oxygen your muscles can consume per minute) has received most of the attention among runners and coaches, a high VO2 max alone is not enough to attain elite-level performances; it simply gains one access into the club, since a runner cannot attain a high level of performance without a high VO2 max. But, while you can improve your VO2 max, it is largely genetically determined. The other two major physiological players of distance running performance -- lactate threshold (LT) and running economy (RE) -- exert a greater influence on your performance and are more responsive to training. I have tested many athletes with an elite-level VO2 max in the laboratory but few of them were capable of running at the elite or even sub-elite level because they did not have a high LT or were not very economical.

From the time of the classic study published in Medicine and Science in Sports and Exercise in 1979 by some of the most prominent names in exercise physiology (Farrell, Wilmore, Coyle, Billing, and Costill), research has shown that the LT is the best physiological predictor of distance running performance. This threshold demarcates the transition between running that is almost purely aerobic and running that includes significant oxygen-independent (anaerobic) metabolism. It represents the fastest speed you can sustain aerobically. (All running speeds have an anaerobic component, although at speeds slower than the LT, that contribution is negligible.) Since the LT represents your fastest sustainable pace, the longer the race, the more important your LT.

Running Economy (RE) is the volume of oxygen consumed at submaximal speeds. In 1930, David Dill and his colleagues were among the first physiologists to suggest that there are marked differences in the amount of oxygen different athletes use when running at the same speeds, and that these differences in "economy" of oxygen use are a major factor explaining differences in running performance of athletes with similar VO2 max values. For example, research has shown that, while Kenyan runners have VO2 max and LT values similar to their American/European counterparts, the Kenyans are more economical, possibly due to their light, non-muscular legs that interestingly resemble those of thoroughbred race horses. The heavier your legs, the more oxygen it takes to move them.

RE is probably even more important than the LT in determining distance running performance because it indicates how hard you're working in relation to your maximum ability to use oxygen. For example, if two runners have a VO2 max of 70 milliliters of oxygen per kilogram of body weight per minute and an LT pace of 7 minutes per mile, but Jack uses 50 and Martin uses 60 milliliters of oxygen while running at 7:30 pace, the pace feels easier for Jack because he is more economical. Therefore, Jack can run faster before using the same amount of oxygen and feeling the same amount of fatigue as Martin. I have yet to see a runner who has superior RE who does not also have a high VO2 max and LT.

1.1 Raise Your Threshold

Sample workouts to raise your lactate threshold (LT):

1. Continuous runs at LT pace, starting at about 3 miles and increasing up to 7 to 8 miles (or about 45 min.) for marathoners.

3. Shorter intervals at slightly faster than LT pace with very short rest periods, such as 2 sets of 4 x 1,000 meters @ 5 to 10 seconds per mile faster than LT pace with 45 seconds rest and two min. rest between sets.

4. Long, slow distance runs with segments run at LT pace (for marathoners), such as 12 to 16 miles with last 2 to 4 miles @ LT pace or 2 miles + 3 miles @ LT pace + 6 miles + 3 miles @ LT pace.

1.1a What's your LT Pace?

LT pace is about 10 to 15 seconds per mile slower than 5K race pace (or about 10K race pace) for slower runners (slower than about 40 minutes for 10K). If using a heart rate (HR) monitor, the pace is about 75 to 80 percent of maximum HR. For highly trained and elite runners, LT pace is about 25 to 30 seconds per mile slower than 5K race pace (or about 15 to 20 seconds per mile slower than 10K race pace) and corresponds to about 85 to 90 percent max HR. For many, it corresponds closely to the race pace they can sustain for one hour. The pace should feel "comfortably hard."

1.2 Improve your economy

Despite its importance, running economy (RE) seems to be the most difficult of the three physiological players (LT, VO2 max and RE) to train. While many runners and coaches think that RE is a reflection of running form, it is more influenced by those microscopic structures that influence oxygen delivery to and use by the muscles -- capillaries and mitochondria, the densities of which are both enhanced with high mileage. Research has shown that runners who run high mileage (more than 70 miles per week) tend to be more economical, which leads one to believe that running high mileage improves RE. In addition to increasing mitochondrial and capillary density, the greater repetition of running movements may result in better biomechanics and muscle fiber recruitment patterns and a synchronization of breathing and stride rate, which may reduce the oxygen cost of breathing. RE may also be improved by the weight loss that often accompanies high mileage, which lowers the oxygen cost. Since VO2 max plateaus with about 70 to 75 miles per week, improved RE may be the most significant attribute gained from running high mileage. However, it's hard to prove cause and effect, since it is not entirely clear whether high mileage runners become more economical by running more miles or are innately more economical and can therefore handle higher mileage.

Other forms of training, like intervals and tempo runs, can also improve RE since, as VO2 max and LT improve, the oxygen cost of any submaximal speed is also likely to improve. However, it is possible to become more economical without improving VO2 max or LT, as research on power training with very heavy weights and plyometrics has shown. Power training focuses on the neural, rather than the metabolic, component of muscle force development to improve RE.

1.3 Boost Your VO2 max

While LT and RE are more important than VO2 max, you don't want to ignore your VO2 max, which is important to reach your running potential and is largely dictated by your stroke volume (the amount of blood your heart pumps with each contraction of its left ventricle) and cardiac output (the amount of blood pumped by your heart each minute). Long intervals provide the heaviest load on the cardiovascular system because of the repeated attainment of the heart's maximum stroke volume and cardiac output (and, by definition, your VO2 max). In lieu of a laboratory test to tell you the velocity at which VO2 max is achieved (vVO2 max), you can use current race performances or heart rate. vVO2 max is close to 1-mile race pace for recreational runners and close to 2-mile race pace (10 to 15 seconds per mile faster than 5K race pace) for highly trained runners. You should be within a few beats of your maximum heart rate by the end of each interval.

Physiology lesson 2.0

Runners with different muscle fibers have different strengths.What It Means For You: Tailor your training to match your muscle fiber composition.

There are two types of runners -- those who have superior speed, whose performance gets better as the race gets shorter, and those who have superior endurance, whose performance gets better as the race gets longer. Despite this, most runners, unless they are individually coached, follow some generic training program. However, those programs don't acknowledge differences in runners' muscle fiber types and their associated metabolic profiles. The types of fibers that make up individual muscles greatly influence your performance.

Humans have three different types of muscle fibers, with gradations between them (see Characteristics of the 3 Muscle Fiber Types). Slow-twitch (ST) fibers are recruited for all of your aerobic runs, while fast-twitch B (FT-B) fibers are only recruited for short anaerobic, high-force production activities, such as sprinting, hurdling, and jumping. Fast-twitch A (FT-A) fibers, which represent a transition between the two extremes of ST and FT-B fibers, are recruited for prolonged anaerobic activities with a relatively high-force output, such as racing 400 meters. It's a given that you have more ST fibers than FT fibers, otherwise you would be a sprinter rather than a distance runner. However, even within a group of distance runners, there is still a disparity in the amount of ST fibers. Some runners may have 90 percent ST and 10 percent FT fibers (marathoners), while others may have 60 percent ST and 40 percent FT fibers (milers).

Understanding your fiber type can help you train smarter. While most runners do the same workouts to focus on a specific race, your training and racing should reflect your physiology. For example, if you have 90 percent ST and 10 percent FT fibers, your best race will likely be the marathon and your training should focus on mileage and tempo runs. If you have 60 percent ST and 40 percent FT fibers, your best race will likely be the 800m or mile, and your training should focus less on mileage and more on interval training. If both runners want to race a 5K or 10K, the former runner should initially do longer intervals, trying to get faster with training, such as 1,200m repeats at 5K race pace, increasing the speed to 3K race pace or decreasing the recovery as training progresses. The latter runner should do shorter intervals, trying to hold the pace for longer with training, such as 800m repeats at 3K race pace, increasing the distance to 1,200 meters or increasing the number of repeats as training progresses. Thus, there can be two paths to meet at the same point.

2.1 What's Your (Muscle) Type?

In lieu of a muscle biopsy to determine your exact muscle fiber type composition, ask yourself the following questions:

1. When you race, a) are you able to hang with your competitors during the middle stages, but get out-kicked in the last quarter to half-mile, or b) do you have a hard time maintaining the pace during the middle stages, but can finish fast and out-kick others?

If you answered (a), you probably have more ST fibers. If you answered (b), you have more FT fibers.

2. Which type of workouts feel easier and more natural -- a) long intervals (800m to mile repeats), long runs, and tempo runs, or b) short, fast intervals (200s and 400s)?

If you answered (a), you have more ST fibers. If you answered (b), you have more FT fibers.

3. Which workouts do you look forward to more -- a) long intervals and tempo runs, or b) short, fast intervals?

If you answered (a), you have more ST fibers. If you answered (b), you have more FT fibers. (People tend to get excited about tasks at which they excel, while being more anxious about tasks that are difficult.)

Physiology lesson 3.0

Metabolism is tightly regulated by enzymes and oxygen.What It Means For You: Develop your aerobic base and do sprint training to enhance enzyme activity that maximizes your running.

Enzymes function as biological catalysts that speed up chemical reactions. In the absence of enzymes, chemical reactions would not occur quickly enough to generate the energy needed to run. The amount of an enzyme also controls which metabolic pathway is used. For example, having more aerobic enzymes will steer the metabolism toward a greater reliance on aerobic metabolism at a given submaximal speed. Enzymes are also activated or inhibited (e.g., their effectiveness in speeding up chemical reactions can be either increased or decreased), determining which metabolic pathways are functional during certain cellular conditions. Thus, enzymes essentially control metabolism and therefore control the pace at which you fatigue.

A number of studies have documented an increase in enzyme activity in response to aerobic training. One of the first among these was published in 1967 in Journal of Biological Chemistry, in which aerobically trained rats increased mitochondrial enzyme activity, increasing the mitochondria's capacity to consume oxygen. More recently, a study published in Journal of Applied Physiology in 2006 found that citrate synthase (a key aerobic enzyme) activity significantly increased by 37 percent in novice runners after 13 weeks of training during which weekly mileage increased from 15 to 36.

Similarly, sprint training induces changes in the anaerobic enzyme profile of muscles and also increases aerobic enzyme activity, particularly when long sprints or short recovery between short sprints are used. For example, a study published in Journal of Applied Physiology in 1998 found that sprint cycle training three times per week for seven weeks using 30-second maximum-effort intervals significantly increased both anaerobic and aerobic enzyme activity. Research on changes in enzyme activity with sprint running is currently lacking.

Metabolism is also regulated by its patriarch -- oxygen. The availability of oxygen determines which metabolic pathway predominates. For example, at the end of the metabolic pathway that breaks down carbohydrates (glycolysis), there is a fork in the road. When there is adequate oxygen to meet the muscle's needs, the final product of glycolysis -- pyruvate -- is converted into an important metabolic intermediate that enters the Krebs cycle for oxidation. This irreversible conversion of pyruvate inside your muscles' mitochondria is a decisive reaction in metabolism since it commits the carbohydrates broken down through glycolysis to be oxidized by the Krebs cycle. However, when there is not adequate oxygen to meet the muscle's needs, pyruvate is converted into lactate. An associated consequence of this latter fate is the accumulation of metabolites and the development of acidosis, causing your muscles to fatigue and you to slow down.

The more aerobically developed you are, by focusing on increasing your mileage and doing LT runs, the more you'll steer pyruvate toward the Krebs cycle and away from lactate production at a given pace. That's a good thing, because the amount of energy you get from pyruvate entering the Krebs cycle is 19 times greater than what you get from pyruvate being converted into lactate. While pyruvate will always be converted into lactate given a fast enough speed, the goal of training is to increase the speed at which that occurs.

Physiology lesson 4.0

The many proponents of diets like Atkins and South Beach would have the public believe that carbohydrates are some kind of poison. Don't listen to them. Carbohydrates are a runner's best friend. Carbohydrates are stored in our skeletal muscles and liver as glycogen, and are also found as sugar (glucose) in the blood. When we run, our bodies use a combination of blood glucose and glycogen as fuel to regenerate the high-energy chemical compound ATP through a process called glycolysis. Endurance performance is strongly influenced by the amount of pre-exercise muscle glycogen, with intense endurance exercise decreasing muscle glycogen content. Carbohydrates are so important that ingesting them during prolonged exercise can even delay fatigue. With the well-documented decrease in muscle glycogen content that accompanies endurance exercise, an empty-refill cycle becomes evident. Since your muscles prefer carbohydrates as fuel, a metabolic priority of recovering muscle is to replenish muscle glycogen stores. And the more your glycogen tank is emptied, the greater it's refilled. Empty a full glass, and you get a refilled larger glass in its place. It's a lot like college fraternity parties.

Glycogen synthesis is controlled by the hormone insulin and the availability and uptake of glucose from the circulation. Insulin, which is secreted from the pancreas, is the primary signal for glycogen synthesis. Through its effect on proteins that transport glucose, insulin draws glucose from the blood into muscle cells. Glucose is then used to make new glycogen, which is simply a branched chain of glucose molecules. The higher the blood insulin concentration and the greater the availability of glucose, the faster glycogen is synthesized and stored.

How do you increase insulin concentration and make glucose available? Consume carbohydrates.

4.1 Got carbs?

Research has shown that the synthesis of glycogen between training sessions occurs most rapidly if carbohydrates are consumed immediately after exercise. Indeed, delaying carbohydrate ingestion for just two hours after a workout significantly reduces the rate at which muscle glycogen is resynthesized and stored. While research suggests that you should consume 0.7 gram of simple carbohydrates (preferably glucose) per pound of body weight (which equals about 7.5 eight-ounce glasses of Gatorade or 3.5 glasses of chocolate milk for a 150-pound runner) within 30 minutes after you run and every two hours for four to six hours to maximize the rate of glycogen synthesis, you don't have to get it all back right away since glycogen will continue to be resynthesized over the 24 hours between workouts.

Despite the many highly advertised commercial sports drinks, any drink that contains a large amount of glucose is great for recovery. For example, my research published in International Journal of Sport Nutrition and Exercise Metabolism in 2006 showed that chocolate milk is just as good or better than other recovery drinks after exhausting exercise. While some studies have found that consuming carbohydrates and protein together also speeds muscle glycogen storage, others have not found this to be the case. The total amount of calories consumed seems to be more important for recovery than the carbohydrate-protein mix. While immediate post-workout carbohydrate ingestion is the best strategy for optimal performance, it may not be the best strategy for runners specifically preparing for the marathon, a race which requires the largest glycogen storage capacity possible, a very efficient capacity to make new glucose, and a very effective system of fat use. Molecular evidence suggests that the opposite strategy -- holding out on the muscles by delaying the consumption of carbohydrates -- may be even more beneficial. By "starving" the muscles of carbohydrates, they are forced to use fat more effectively and even more glycogen may be synthesized when carbohydrates are finally introduced.

Low muscle glycogen content has been shown to enhance the transcription of genes involved in protein synthesis. Think of this strategy as creating a threat to the muscles' survival: When you threaten the survival of muscles by depriving them of their preferred fuel, a strong signal is sent to make more of that fuel to combat the threat and to use other sources of fuel more effectively. The downside to training in a low-glycogen state, however, is that it's hard to maintain a high intensity since such high-intensity running is dependent on carbohydrates for fuel. A lot more research needs to be done in this area, but if you're going to try training with low muscle glycogen, make sure you consume lots of carbs before your marathon, so you "train low, race high."